Refractory pembrolizumab immunotherapy-related colitis requiring biological therapy in an inactive HBcAb carrier.

Immune checkpoint inhibitors are a class of cancer immunotherapy, with a constellation of side effects that require early recognition and management. We present a patient with metastatic adenocarcinoma started on pembrolizumab a month prior, who was admitted to the hospital for bloody diarrhoea. He underwent flexible sigmoidoscopy with biopsy proven grade 3 immune-mediated diarrhoea and colitis. He developed progressively worsening diarrhoea despite appropriate intravenous corticosteroids therapy, and initiation of corticosteroid-sparing therapy was complicated by discovery of hepatitis B core antibodies indicating a chronic hepatitis B carrier state. We discuss our work-up of new onset haemorrhagic diarrhoea in a patient on immunotherapy for metastatic non-small cell lung cancer, as well as a review of current guidelines for antiviral prophylaxis in these patients.